“The review showed that most of the names – 89.1 percent – were invalid, either because the person was not found on voter registration rolls or the signature and address did not match those on file,” said Dave Ammons, spokesman for Secretary of State Sam Reed.

The state has asked the Washington State Patrol to investigate. Initiative signature fraud is a Class C felony punishable by up to five years in prison and a fine of up to $10,000.

“This is the worst case of attempted signature fraud we have seen in modern times. It may be only a tiny percentage of the total signatures, but it does represent an attack on the process, which relies greatly on the integrity of the people who circulate the petitions. For that reason, we are bringing the full force of the law to bear,” Reed said in a statement.

On Thursday, state officials said I-1098 had qualified for the November ballot, with more than enough valid signatures.

I-1098, which is championed by Bill Gates, Sr., would tax couples with adjusted gross incomes greater than $400,000 annually, or incomes of more than $200,000 for individuals. Supporters say that represents the top 3 percent of earners in Washington. It also would cut the state property tax by 20 percent and increase the business-and-occupation tax credit to $4,800. Supporters say it would bring in about $1 billion per year for education and health programs.